Presently blood gas and electrolyte measurements during cardiopulmonary bypass (CPB) are made on discrete blood samples drawn at various intervals. Although this is usually sufficient, it is not adequate during an acute crisis. It is also highly probable, particularly in older patients, patients with multiorgan dysfunction and possibly even patients without other complications, that recovery time will be less eventful with more precise monitoring of blood gases and electrolytes during CPB. The purpose of this project is to develop a multiple on line sensor system to measure PO2, pH, PCO2, and K+ during CPB. The sensor will be constructed using existing technology including the Biochem's exclusive technology on H+ selective polymer membrane and metal-metal oxide. Biochem presently is making the following products; a non-glass polymeric pH, and dual function pH/PCO2 sensor for intravascular measurement, a muscle-tissue pH sensor, transcutaneous O2 and CO2 sensors, and ion selective K+ membrane intravascular and muscle-tissue sensors. The challenge is to configure these into a system usable for monitoring these parameters during cardiopulmonary bypass. This will include drawings of and construction of prototypes, testing of the system in an artificial model, laboratory testing in an animal model, and re-evaluation of the system configuration prior to initiation of a model for clinical testing. The system must be stable and reliable. On line calibration is essential. It must meet requirements for clinical use, be compact and easy to use. This study will initiate a program with the goal of more effective and less expensive continuous blood gas and electrolytes monitoring during circulatory assistance.